In undersea fluid extraction systems, operational efficiency can be improved by the use of submersible pumps, in particular where production is from wells remote from a mother platform or fluid processing facility, so that the well effluent requires to be transported over substantial distances. Submersible pumps could also be used in multi-phase marginal field wells where the fluid is monophasic downhole. However electrically powered submersible pumps tend to be very prone to breakdown and are generally unreliable. Average operational times before failure may be only a few months. More often than not, failure is due to a damaged external power cable. Such pumps are accordingly unattractive economically because of the cost of frequent well shut-downs.
The present invention is concerned accordingly with the provision of a submersible pump system for subsea use which avoids the above-mentioned disadvantage.